2,303 research outputs found
Detecting dark matter-dark energy coupling with the halo mass function
We use high-resolution simulations of large-scale structure formation to
analyze the effects of interacting dark matter and dark energy on the evolution
of the halo mass function. Using a chi-square likelihood analysis, we find
significant differences in the mass function between models of coupled dark
matter-dark energy and standard concordance cosmology Lambda-CDM out to
redshift z=1.5. We also find a preliminary indication that the Dark Energy
Survey should be able to distinguish these models from Lambda-CDM within its
mass and redshift contraints. While we can distinguish the effects of these
models from Lambda-CDM cosmologies with different fundamental parameters, DES
will require independent measurements of sigma-8 to confirm these effects.Comment: 5 pages, 3 figures, responded to referee comments, accepted by Ap
Cluster magnetic fields from active galactic nuclei
Active galactic nuclei (AGN) found at the centers of clusters of galaxies are
a possible source for weak cluster-wide magnetic fields. To evaluate this
scenario, we present 3D adaptive mesh refinement MHD simulations of a cool-core
cluster that include injection of kinetic, thermal, and magnetic energy via an
AGN-powered jet. Using the MHD solver in FLASH 2, we compare several
sub-resolution approaches that link the estimated accretion rate as measured on
the simulation mesh to the accretion rate onto the central black hole and the
resulting feedback. We examine the effects of magnetized outflows on the
accretion history of the black hole and discuss the ability of these models to
magnetize the cluster medium.Comment: 4 pages, 2 figures, submitted to conference proceedings "The
Monster's Fiery Breath: Feedback in Groups, Galaxies, and Clusters
The Influence of AGN Feedback on Galaxy Cluster Observables
Galaxy clusters are valuable cosmological probes. However, cluster mass
estimates rely on observable quantities that are affected by complicated
baryonic physics in the intracluster medium (ICM), including feedback from
active galactic nuclei (AGN). Cosmological simulations have started to include
AGN feedback using subgrid models. In order to make robust predictions, the
systematics of different implementations and parametrizations need to be
understood. We have developed an AGN subgrid model in FLASH that supports a few
different black hole accretion models and feedback models. We use this model to
study the effect of AGN on X-ray cluster observables and its dependence on
model variations.Comment: minor error corrected, to appear in proceedings of the conference
"The Monster's Fiery Breath: Feedback in Galaxies, Groups, and Clusters",
June 2009, Madison, Wisconsi
The Impact of Type Ia Supernova Ejecta on Binary Companions
We present adaptive mesh refinement (AMR) hydrodynamical simulations of the
interaction between Type Ia supernovae and their companion stars within the
context of the single-degenerate model. Results for 3D red-giant companions
without binary evolution agree with previous 2D results by Marietta et al. We
also consider evolved helium-star companions in 2D. For a range of helium-star
masses and initial binary separations, we examine the mass unbound by the
interaction and the kick velocity delivered to the companion star. We find that
unbound mass versus separation obeys a power law with index between -3.1 and
-4.0, consistent with previous results for hydrogen-rich companions. Kick
velocity also obeys a power-law relationship with binary separation, but the
slope differs from those found for hydrogen-rich companions. Assuming accretion
via Roche-lobe overflow, we find that the unbound helium mass is consistent
with observational limits. Ablation (shock heating) appears to be more
important in removing gas from helium-star companions than from hydrogen-rich
ones, though stripping (momentum transfer) dominates in both cases.Comment: 6 pages, 2 figures, to appear in the proceedings of the conference
"Binary Star Evolution: Mass Loss, Accretion, and Mergers" at Mykonos,
Greece, June 22-25, 201
A Direct Multigrid Poisson Solver for Oct-Tree Adaptive Meshes
We describe a finite-volume method for solving the Poisson equation on
oct-tree adaptive meshes using direct solvers for individual mesh blocks. The
method is a modified version of the method presented by Huang and Greengard
(2000), which works with finite-difference meshes and does not allow for shared
boundaries between refined patches. Our algorithm is implemented within the
FLASH code framework and makes use of the PARAMESH library, permitting
efficient use of parallel computers. We describe the algorithm and present test
results that demonstrate its accuracy.Comment: 10 pages, 6 figures, accepted by the Astrophysical Journal; minor
revisions in response to referee's comments; added char
A first estimate of radio halo statistics from large-scale cosmological simulation
We present a first estimate based on a cosmological gasdynamics simulation of
galaxy cluster radio halo counts to be expected in forthcoming low-frequency
radio surveys. Our estimate is based on a FLASH simulation of the LCDM model
for which we have assigned radio power to clusters via a model that relates
radio emissivity to cluster magnetic field strength, intracluster turbulence,
and density. We vary several free parameters of this model and find that radio
halo number counts vary by up to a factor of two for average magnetic fields
ranging from 0.2 to 3.1 uG. However, we predict significantly fewer
low-frequency radio halos than expected from previous semi-analytic estimates,
although this discrepancy could be explained by frequency-dependent radio halo
probabilities as predicted in reacceleration models. We find that upcoming
surveys will have difficulty in distinguishing models because of large
uncertainties and low number counts. Additionally, according to our modeling we
find that expected number counts can be degenerate with both reacceleration and
hadronic secondary models of cosmic ray generation. We find that relations
between radio power and mass and X-ray luminosity may be used to distinguish
models, and by building mock radio sky maps we demonstrate that surveys such as
LOFAR may have sufficient resolution and sensitivity to break this model
degeneracy by imaging many individual clusters.Comment: 18 pages, 14 figures, revised from referee comments, ApJ accepted,
public catalog available at
http://sipapu.astro.illinois.edu/http://sipapu.astro.illinois.edu/foswiki/bin/view/Main/RadioHaloMap
Rings of Dark Matter in Collisions Between Clusters of Galaxies
Several lines of evidence suggest that the galaxy cluster Cl0024+17, an
apparently relaxed system, is actually a collision of two clusters, the
interaction occurring along our line of sight. Recent lensing observations
suggest the presence of a ring-like dark matter structure, which has been
interpreted as the result of such a collision. In this paper we present
-body simulations of cluster collisions along the line of sight to
investigate the detectability of such features. We use realistic dark matter
density profiles as determined from cosmological simulations. Our simulations
show a "shoulder" in the dark matter distribution after the collision, but no
ring feature even when the initial particle velocity distribution is highly
tangentially anisotropic (). Only when the initial
particle velocity distribution is circular do our simulations show such a
feature. Even modestly anisotropic velocity distributions are inconsistent with
the halo velocity distributions seen in cosmological simulations, and would
require highly fine-tuned initial conditions. Our investigation leaves us
without an explanation for the dark matter ring-like feature in Cl 0024+17
suggested by lensing observations.Comment: 7 pages (emulateapj), 9 figures. Expanded figures and text to match
accepted versio
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